The present invention relates to a multi-element rotor blade, and more particularly to geometry for a leading edge slat.
Multi-element airfoils are in common use on fixed wing aircraft. In such conventional applications, the aerodynamic flow environment is steady or quasi-steady. These airfoil sections are designed specifically for high angles of attack (AOA) and low Mach number conditions since at higher speeds the additional elements are retracted.
Multi-element airfoils offer the potential for a significant breakthrough in rotor performance by providing a higher maximum lift coefficient. Increased lift coefficient enables the rotor to achieve a higher thrust and/or higher flight speeds, impacting the payload/range, maneuverability, reduced tip speed and lower noise signature for rotary-wing aircraft. Multi-element airfoil application to rotary-wing aircraft has concentrated upon the development of fixed elements which attempt to provide a compromise between achieving an average improvement to rotor disc lift while avoiding an unacceptable increase in drag. Fixed elements provide numerous design challenges including the aerodynamic requirements from lower-speed, high angle of attack on the retreating side of the rotor disc to high speed, low angle of attack operation on the advancing side of the rotor disc.
Current designs for high lift in the low speed regime suffer from unacceptable drag levels at high speed while current designs for low drag in the high-speed regime do not show sufficient benefits of increased lift in the low speed regime.
Accordingly, it is desirable to provide a slat shape for multi-element rotor blade airfoils, which maximizes lift performance while minimizing drag in unsteady aerodynamic flow environment and various flight regimes.